"Hidden gem" is a bit tough since pretty much every restaurant in Disney has its fans. That aside, here are a few that might not have made your radar.
Sanaa - Simply one of the best TS on property when factoring for value, service, taste, and uniqueness. As another said, the bread service is wonderful--worth the effort alone. It makes a great and filling lunch which is generally the best time to see the animals.
Artist Point - To many, it's a bit out of the way. Good. That way it remains one of the easiest Signatures to for which to get an ADR. And it's usually a superb experience.
The Wave - Solid to good food, easy access to/from MK.
Il Mulino - Excellent Italian for the most part. Offers small plates which is good for smaller appetites.